The present invention relates generally to separable connector modules for electrical power cables and particularly to a type of module commonly used in high voltage underground electric power distribution systems to connect the cables and operating components of such a system. Electrical power cables used in underground power distribution are commonly provided with waterproof connector modules at their ends. These modules may connect cable-to-cable or cable-to-component, such as to a transformer bushing terminal. In general, such modules consist of a matching pair of male and female contacts each disposed inside a separate and matching insulating housing. The insulating housings are mated together in matching relationship to provide a waterproof and stress-relieving connection. Such modules are commonly disconnected from a live circuit, despite certain arcing hazards known to be involved in such a loadbreak procedure. They are therefor generally designed to minimize certain of these hazards.
The male contact is a conducting rod having an end portion known as an arc-follower made of a material which, in response to arcing across its surface, gives off arc extinguishing gases.
The female contact generally includes a resilient conductive grasping member for making firm electrical contact to the rod of the male contact.
The rod is guided to the female contact by a bore provided in the insulating portion of the housing. Behind the female contact assembly, there may be a gas pressure chamber for holding excess gas generated during disconnection. The bore of the female contact module may be provided with a replaceable bore sleeve having an inside liner of arc extinguishing material.
When the rod is pulled from the female contact and out through the bore in the disconnecting process, an arc is drawn between the rod and the female contact. This arc plays over the arc extinguishing material of the bore sleeve liner and the arc-follower to generate arc-extinguishing gases. These gases appear suddenly and can, at relatively high voltages of, for instance, 13 kilovolts, result in sudden high gas pressure inside the bore. The generated gas plays an essential role in extinguishing the arc before the rod is pulled from the bore.
A common failure mode of the type of connector module described above is that during the disconnection process, some of the hot ionized gases generated by the arcing inside the module escape from the module as the rod is being removed from the bore to result in the establishing of an arc outside the module. Once such an arch through outside air is established it cannot be extinguished and tends to jump to a nearby grounded object to produce a short circuit.
Various means have been devised for minimizing the escape of hot arc-generated from the module upon disconnection. Examples of such means are described, for instance, in the following:
U.s. pat. Nos. 3,587,035 issued June 22, 1971 to E. J. Kotski; 3,539,972 issued Nov. 10, 1970 to Reute et al.; 3,542,986 issued Nov. 24, 1970 to E. J. Kotski; PA1 U.s. pat. application Ser. No. 160,798 filed July 8, 1971 entitled "Electric Cable Termination Module Having a Gas Trap Valve" and assigned to General Electric Company. PA1 U.s. pat. application Ser. No. 181,416 filed September 17, 1971, entitled "Electric Circuit Interrupter Having Means Restricting Flow of Arc Generated Gases Therefrom" now abandoned in favor of a continuation application Ser. No. 387,759 filed Aug. 13, 1973, also now abandoned in favor of a continuation application Ser. No. 514,949 filed Oct. 15, 1974, all assigned to General Electric Company.
The approaches to preventing the escape of hot arc-generated gases from the module on disconnection include installing gas retaining gaskets near the inside end of the bore to prevent the gases from rushing out between the rod and the bore sleeve liner.
In addition to the gaskets near the end of the bore, there may be provided a gas trap valve which prevents gases from leaving the bore after the arc-follower has left the bore. Also, a gas retaining chamber can be provided in order to prevent excessive pressure build-up which would increase the amount of escaping gas.
After a number of disconnections, female contacts of the module of the type described above generally become damaged by the arcing that takes place at each disconnection. It is therefore common practice to manufacture the female contact integrally with a cylindrical bore sleeve as a replaceable sleeve and contact unit. The sleeve and contact unit may be screwed into the housing.
It has been found, however, that modules having such a replaceable bore sleeve unit are subject to a failure mode of the gas restrike type even, when provided with all three of the above-described prior features for preventing the escape of hot arc-generated gas from the module.